1. Field of the Invention
The present invention relates to material analysis, and particularly to a measuring method for predicting the property values of complex hydrocarbon fuels, such as the property values of gasoline by distillation. More particularly, the present invention relates to compensation of boiling point distribution measurements used for the prediction of physical properties of hydrocarbons.
2. Description of the Related Art
Petroleum products, such as gasoline, are typically formulated as blends consisting of thousands of chemical compounds. For a wide variety of applications, it is desirable to be able to identify and quantify each of these components. These products are generally identified and classified based on some of the bulk properties, such as, for example, the range of distillation, density, and the cetane number, viscosity, pour point, API gravity and the like. These data are useful both during production of such fuels at the refinery and also during delivery of such fuels to the end-user. In either case, with these data, the producer, for production control purposes, or the consumer, to meet engine requirements or for comparative purposes, can assess the quality or value of the particular product. It is therefore of great interest to be able to ascertain, with specificity, the properties of hydrocarbon-based fuels.
Many characterizing properties or attributes, such as Reid vapor pressure, viscosity, refractive index, hydrogen-to-carbon (H/C) content, paraffin, naphthene and aromatic (PNA) content, aniline point, octane number, freezing point, cloud point, smoke point, diesel index, refractive index, cetane index, and the like are generally measured for a crude oil or only certain of its fractions according to well-specified ASTM tests.
Detailed characterization of petroleum fuels entails the use of sophisticated analytical equipment, such as gas chromatography (GC) and nuclear magnetic resonance (NMR). Although it is possible to obtain detailed molecular and structural composition of petroleum fractions using GC-MS and NMR techniques on the order of a few days, these extensive experimental programs can be complex, expensive and overly consuming in terms of both time and computing power. Because of the issues involved, these analytical methods do not find wide acceptance in daily refinery operations.
Accurate characterization of petroleum fuels is an important step in the application of kinetic and thermodynamic calculations for the design, operation, and simulation of petroleum refining processes. An insufficient description of heavier hydrocarbons (e.g., pentane and heavier; C5+) reduces the accuracy of predictions. Unfortunately, complete experimental data on the C5+ hydrocarbon fraction are seldom available. Ideally, fuel properties are determined experimentally in the laboratory on actual fluid samples taken from the process under study. Because of the expense of the experimental determination of such data, there is interest in their accurate prediction.
In order to speed up the execution of real-time simulation, it would desirable to be able to utilize a series of simplified correlations for the evaluation of physical properties of petroleum fractions. Using available data, present methods require as input parameters the fuel global properties, such as the average boiling point, the specific gravity and some characterization factors. Unfortunately, with these input requirements, the models are not suitable for incorporation into the latest generation of molecularly explicit simulation models. In addition, wide boiling range fractions are mixtures of a large number of hydrocarbon compounds, the types of which vary along the distillation curve, therefore a single value for boiling point or specific gravity does not characterize the fraction very well. Moreover, as many existing correlations are based on properties of pure compounds, errors in predicted values from the correlations increase significantly when the methods are applied to mixtures.
Distillation curves provide a breadth of information about the crude oil or the petroleum fuel. In certain respects, the boiling point distribution is representative of the composition of the petroleum fraction. Therefore, in principle, by determining the presence and volume percent of the components in a conventional hydrocarbon fuel solution, the overall physical properties can be determined.
There are many types of standard distillation tests that determine the boiling point distribution of petroleum fuels, the inter-conversion between which is well documented. Some of the more common standard test methods for distillation of petroleum products include: ASTM D86-96, which is performed under atmospheric pressure and is used for determining the boiling point distribution of light petroleum fractions, such as naphtha, kerosene, diesel, and light gas oil; micro-distillation; molecular distillation; fractional distillation (typically using a spinning band still); ASTM D5236 distillation (typically using a pot still); D1160 (for heavy petroleum fractions); ASTM D3710 (simulated distillation, which is also known as the GC SimDist method, and uses gas chromatography to determine the true boiling point, or TBP, of gasoline); ASTM D2887 (GC SimDist to determine the TBP of petroleum fraction other than gasoline); ASTM D2892 (also known as 15/5 distillation, which produces simulated TBP of petroleum fuels using a distillation column with 15 theoretical plates and a reflux ratio of 5); ASTM D5236 Distillation (also known as the vacuum pot still method, and is used for heavy hydrocarbon mixtures); ASTM D5307 (SimDist for determining TBP of crude oil); ASTM D6352-98; and Hemple analysis for the distillation of a large volume of fuel samples providing further detailed analysis of the produced distilled cuts. ASTM D86-96 and D1160 may be combined together for determining the boiling point distribution of wide boiling range materials, such as crude oils.
In a distillation device operated according to the ASTM D86 standard test method, for example, a 100 ml petroleum sample, placed in a flask, is heated at a regulated rate, so that a uniform average rate of condensation in mL/min is maintained. This rate varies from zero to five volume % recovered, from 5 to 10 volume % recovered, and so on. When the first drop appears at the lower end of the condenser tube, the thermometer reading (vapor temperature) is recorded as the initial boiling point (IBP). Temperature readings are recorded at several volume % distilled (as shown in Table 1 below), up to the final boiling point (FBP) and heating is discontinued.
After the flask has cooled, the volume of remaining liquid is measured and recorded as the recovery. For heavy fractions, heating is discontinued when the decomposition point is observed, and the vapor reaches a maximum temperature and then starts declining before the end point. The volume increments for the reported boiling point distribution by the ASTM distillation apparatus is user-selected, and Table 1 illustrates one such example:
TABLE 1Data output from ASTM D86 distillation testVol %T (° F.)0IBP10T10%30T30%50T50%70T70%90T90%100FBPRecovery~98%
Traditionally, the analytical methods that relate to determining petroleum properties in hydrocarbons take a long time to carry out and are thus very time-consuming. In the laboratory, the properties are measured using numerous and varying types of analytical and physical test equipment, with skilled personnel being required to perform the testing. For each experimentally determined property, there is at least one apparatus, thus for 30 properties there is a need for 30 separate experimental apparatuses. Such equipment is very expensive, requires frequent maintenance, and also requires the availability of many samples of the fuel, along with taking between several minutes and several hours per sample to run the tests.
Thus, a system and method for measuring the properties of petroleum fuels by distillation solving the aforementioned problems is desired.